Ultrafine Antimony Nanocrystals/Phosphorus Pitaya-Like Nanocomposites as Anodes for High-Performance Sodium-Ion Batteries

Ultrafine (3-S nm in diameters) antimony (Sb) nanocrystals embedded in phosphorus (P) pitaya-like nanocomposites (Sb/P composites) were fabricated via a facile chemical precipitation synthesis. In this pitaya-like structure, P as a buffer matrix could effectively mitigate volume expansion/contraction of Sb and enhance the structural integrity during the Na+-insertion/extraction process. Moreover, P acted as an active material to contribute capacity for the overall active material, resulting in Na-ion storage capacity higher than that of mono-Sb. When regarded as anode materials, Sb/P nanocomposites delivered a capacity of 795.9 mA h g(-1) and maintained great cyclability (478.1 mA h g(-1) at 800 mA g(-1) over 500 cycles). Furthermore, the rate capability (341.5 mA h g(-1) at 32 A g(-1)) was better than the reported literature under higher current density. Most importantly, operando X-ray diffraction and ex situ transmission electron microscopy results were carried out to investigate the structural evolutions of Sb/P, indicating the electrochemical mechanism of the Na3Sb and Na3P alloys during the cycling process, which imply that both Sb and P in the nanocomposite could react with Na ions completely. This work possesses an innovative material morphology and replaces the general carbon-based buffer matrix with phosphorus so that the pitaya-like Sb/P composites may become a good alternative in a Na-ion system.